_______________General DescriptionThe MAX7219/MAX7221 are compact, serial input/out-put common-cathode display drivers that interface microprocessors (µPs) to 7-segment numeric LED dis-plays of up to 8 digits, bar-graph displays, or 64 indi-vidual LEDs. Included on-chip are a BCD code-B decoder, multiplex scan circuitry, segment and digit drivers, and an 8x8 static RAM that stores each digit.Only one external resistor is required to set the seg-ment current for all LEDs. The MAX7221 is compatible with SPI™, QSPI™, and Microwire™, and has slew-rate-limited segment drivers to reduce EMI.A convenient 3-wire serial interface connects to all common µPs. Individual digits may be addressed and updated without rewriting the entire display. The MAX7219/MAX7221 also allow the user to select code-B decoding or no-decode for each digit.The devices include a 150µA low-power shutdown mode, analog and digital brightness control, a scan-limit register that allows the user to display from 1 to 8digits, and a test mode that forces all LEDs on.________________________ApplicationsBar-Graph Displays 7-Segment Displays Industrial Controllers Panel Meters LED Matrix Displays____________________________Featureso 10MHz Serial Interfaceo Individual LED Segment Control o Decode/No-Decode Digit Selectiono 150µA Low-Power Shutdown (Data Retained)o Digital and Analog Brightness Control o Display Blanked on Power-Up o Drive Common-Cathode LED Display o Slew-Rate Limited Segment Drivers for Lower EMI (MAX7221)o SPI, QSPI, Microwire Serial Interface (MAX7221)o 24-Pin DIP and SO PackagesMAX7219/MAX7221Serially Interfaced, 8-Digit LED Display Drivers________________________________________________________________Maxim Integrated Products1________Typical Application Circuit__________________Pin Configuration19-4452; Rev 3; 7/97SPI and QSPI are trademarks of Motorola Inc. Microwire is a trademark of National Semiconductor Corp.For free samples & the latest literature: , or phone 1-800-998-8800.For small orders, phone 408-737-7600 ext. 3468.M A X 7219/M A X 72212_______________________________________________________________________________________ABSOLUTE MAXIMUM RATINGSELECTRICAL CHARACTERISTICS(V+ = 5V ±10%, R SET = 9.53k Ω±1%, T A = T MIN to T MAX , unless otherwise noted.)Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.Voltage (with respect to GND)V+............................................................................-0.3V to 6V DIN, CLK, LOAD, CS ...............................................-0.3V to 6V All Other Pins.............................................-0.3V to (V+ + 0.3V)CurrentDIG0–DIG7 Sink Current................................................500mA SEGA–G, DP Source Current.........................................100mA Continuous Power Dissipation (T A = +85°C)Narrow Plastic DIP..........................................................0.87W Wide SO..........................................................................0.76W Narrow CERDIP.................................................................1.1WOperating Temperature RangesMAX7219C_G/MAX7221C_G ..............................0°C to +70°C MAX7219E_G/MAX7221E_G............................-40°C to +85°C Storage Temperature Range.............................-65°C to +160°C Lead Temperature (soldering, 10sec).............................+300°CMAX7219/MAX7221_______________________________________________________________________________________3ELECTRICAL CHARACTERISTICS (continued)(V+ = 5V ±10%, R SET =9.53k Ω±1%, T A = T MIN to T MAX , unless otherwise noted.)M A X 7219/M A X 72214_________________________________________________________________________________________________________________________________Typical Operating Characteristics(V+ = +5V, T A = +25°C, unless otherwise noted.)730750740770760790780800820810830 4.04.44.85.25.66.0SCAN FREQUENCY vs. POSITIVE SUPPLY VOLTAGEM A X 7219/21 01POSITIVE SUPPLY VOLTAGE (V)S C A N F R E Q U E N C Y (H z )20104030605070012345SEGMENT DRIVER OUTPUT CURRENTvs. OUTPUT VOLTAGEOUTPUT VOLTAGE (V)O U T P U T C U R R E N T (m A )MAX7219SEGMENT OUTPUT CURRENTM A X 7219/21 035µs/div10mA/div0MAXIMUM INTENSITY = 31/32MAX7221SEGMENT OUTPUT CURRENTM A X 7219/21 045µs/div10mA/divMAXIMUM INTENSITY = 15/16MAX7219/MAX7221______________________________________________________________Pin Description_________________________________________________________Functional DiagramM A X 7219/M A X 72216______________________________________________________________________________________________________Detailed DescriptionMAX7219/MAX7221 DifferencesThe MAX7219 and MAX7221 are identical except fortwo parameters: the MAX7221 segment drivers are slew-rate limited to reduce electromagnetic interfer-ence (EMI), and its serial interface is fully SPI compati-ble.Serial-Addressing ModesFor the MAX7219, serial data at DIN, sent in 16-bit packets, is shifted into the internal 16-bit shift register with each rising edge of CLK regardless of the state of LOAD. For the MAX7221, CS must be low to clock data in or out. The data is then latched into either the digit or control registers on the rising edge of LOAD/CS .LOAD/CS must go high concurrently with or after the 16th rising clock edge, but before the next rising clock edge or data will be lost. Data at DIN is propagated through the shift register and appears at DOUT 16.5clock cycles later. Data is clocked out on the falling edge of CLK. Data bits are labeled D0–D15 (Table 1).D8–D11 contain the register address. D0–D7 contain the data, and D12–D15 are “don’t care” bits. The first received is D15, the most significant bit (MSB).Digit and Control RegistersTable 2 lists the 14 addressable digit and control regis-ters. The digit registers are realized with an on-chip,8x8 dual-port SRAM. They are addressed directly so that individual digits can be updated and retain data as long as V+ typically exceeds 2V. The control registers consist of decode mode, display intensity, scan limit (number of scanned digits), shutdown, and display test (all LEDs on).Shutdown ModeWhen the MAX7219 is in shutdown mode, the scan oscil-lator is halted, all segment current sources are pulled to ground, and all digit drivers are pulled to V+, thereby blanking the display. The MAX7221 is identical, except the drivers are high-impedance. Data in the digit and control registers remains unaltered. Shutdown can be used to save power or as an alarm to flash the display by successively entering and leaving shutdown mode. For minimum supply current in shutdown mode, logic inputs should be at ground or V+ (CMOS-logic levels).Typically, it takes less than 250µs for the MAX7219/MAX7221 to leave shutdown mode. The display driver can be programmed while in shutdown mode, and shutdown mode can be overridden by the display-test function.Figure 1. Timing DiagramTable 1. Serial-Data Format (16 Bits)Initial Power-UpOn initial power-up, all control registers are reset, the display is blanked, and the MAX7219/MAX7221 enter shutdown mode. Program the display driver prior to display use. Otherwise, it will initially be set to scan one digit, it will not decode data in the data registers, and the intensity register will be set to its minimum value.Decode-Mode RegisterThe decode-mode register sets BCD code B (0-9, E, H,L, P, and -) or no-decode operation for each digit. Each bit in the register corresponds to one digit. A logic high selects code B decoding while logic low bypasses the decoder. Examples of the decode mode control-regis-ter format are shown in Table 4.When the code B decode mode is used, the decoder looks only at the lower nibble of the data in the digit registers (D3–D0), disregarding bits D4–D6. D7, which sets the decimal point (SEG DP), is independent of the decoder and is positive logic (D7 = 1 turns the decimal point on). Table 5 lists the code B font.When no-decode is selected, data bits D7–D0 corre-spond to the segment lines of the MAX7219/MAX7221.Table 6 shows the one-to-one pairing of each data bit to the appropriate segment line.MAX7219/MAX7221Table 3. Shutdown Register Format (Address (Hex) = XC)Table 4. Decode-Mode Register Examples (Address (Hex) = X9)M A X 7219/M A X 7221Intensity Controland Interdigit BlankingThe MAX7219/MAX7221 allow display brightness to be controlled with an external resistor (R SET ) connected between V+ and ISET. The peak current sourced from the segment drivers is nominally 100 times the current entering ISET. This resistor can either be fixed or vari-able to allow brightness adjustment from the front panel. Its minimum value should be 9.53Ω, which typi-cally sets the segment current at 40mA. Display bright-ness can also be controlled digitally by using the intensity register.Digital control of display brightness is provided by an internal pulse-width modulator, which is controlled by the lower nibble of the intensity register. The modulator scales the average segment current in 16 steps from a maximum of 31/32 down to 1/32 of the peak current set by R SET (15/16 to 1/16 on MAX7221). Table 7 lists the intensity register format. The minimum interdigit blank-ing time is set to 1/32 of a cycle.8_______________________________________________________________________________________Table 5. Code B FontTable 6. No-Decode Mode Data Bits and Corresponding Segment Lines*The decimal point is set by bit D7 = 1Scan-Limit RegisterThe scan-limit register sets how many digits are dis-played, from 1 to 8. They are displayed in a multiplexed manner with a typical display scan rate of 800Hz with 8digits displayed. If fewer digits are displayed, the scan rate is 8f OSC /N, where N is the number of digitsscanned. Since the number of scanned digits affects the display brightness, the scan-limit register should not be used to blank portions of the display (such as leading zero suppression). Table 8 lists the scan-limit register format.MAX7219/MAX7221_______________________________________________________________________________________9Table 7. Intensity Register Format (Address (Hex) = XA)Table 8. Scan-Limit Register Format (Address (Hex) = XB)*See Scan-Limit Register section for application.M A X 7219/M A X 7221If the scan-limit register is set for three digits or less,individual digit drivers will dissipate excessive amounts of power. Consequently, the value of the R SET resistor must be adjusted according to the number of digits dis-played, to limit individual digit driver power dissipation.Table 9 lists the number of digits displayed and the corresponding maximum recommended segment cur-rent when the digit drivers are used.Display-Test RegisterThe display-test register operates in two modes: normal and display test. Display-test mode turns all LEDs on by overriding, but not altering, all controls and digit reg-isters (including the shutdown register). In display-test mode, 8 digits are scanned and the duty cycle is 31/32(15/16 for MAX7221). Table 10 lists the display-test reg-ister format.No-Op RegisterThe no-op register is used when cascading MAX7219s or MAX7221s. Connect all devices’ LOAD/CS inputs together and connect DOUT to DIN on adjacent devices. DOUT is a CMOS logic-level output that easily drives DIN of successively cascaded parts. (Refer to the Serial Addressing Modes section for detailed infor-mation on serial input/output timing.) For example, if four MAX7219s are cascaded, then to write to thefourth chip, sent the desired 16-bit word, followed by three no-op codes (hex XX0X, see Table 2). When LOAD/CS goes high, data is latched in all devices. The first three chips receive no-op commands, and the fourth receives the intended data.__________Applications InformationSupply Bypassing and WiringTo minimize power-supply ripple due to the peak digit driver currents, connect a 10µF electrolytic and a 0.1µF ceramic capacitor between V+ and GND as close to the device as possible. The MAX7219/MAX7221 should be placed in close proximity to the LED display, and connections should be kept as short as possible to minimize the effects of wiring inductance and electro-magnetic interference. Also, both GND pins must be connected to ground.Selecting R SET Resistor andUsing External DriversThe current per segment is approximately 100 times the current in ISET. To select R SET , see Table 11. The MAX7219/MAX7221’s maximum recommended seg-ment current is 40mA. For segment current levels above these levels, external digit drivers will be need-ed. In this application, the MAX7219/MAX7221 serve only as controllers for other high-current drivers or tran-sistors. Therefore, to conserve power, use R SET = 47k Ωwhen using external current sources as segment dri-vers.The example in Figure 2 uses the MAX7219/MAX7221’s segment drivers, a MAX394 single-pole double-throw analog switch, and external transistors to drive 2.3”AND2307SLC common-cathode displays. The 5.6V zener diode has been added in series with the decimal point LED because the decimal point LED forward volt-age is typically 4.2V. For all other segments the LED forward voltage is typically 8V. Since external transis-tors are used to sink current (DIG 0 and DIG 1 are used as logic switches), peak segment currents of 45mA are allowed even though only two digits are displayed. In applications where the MAX7219/MAX7221’s digit dri-vers are used to sink current and fewer than four digits are displayed, Table 9 specifies the maximum allow-able segment current. R SET must be selected accord-ingly (Table 11).Refer to the Power Dissipation section of the Absolute Maximum Ratings to calculate acceptable limits for ambient temperature, segment current, and the LED forward-voltage drop.10______________________________________________________________________________________Table 9. Maximum Segment Current for 1-, 2-, or 3-Digit DisplaysTable 10. Display-Test Register Format (Address (Hex) = XF)Note: The MAX7219/MAX7221 remain in display-test mode (all LEDs on) until the display-test register is reconfigured for normal operation.Computing Power DissipationThe upper limit for power dissipation (PD) for the MAX7219/MAX7221 is determined from the following equation:PD = (V + x 8mA) + (V+ - V LED )(DUTY x I SEG x N)where:V+ = supply voltageDUTY = duty cycle set by intensity register N = number of segments driven (worst case is 8)V LED = LED forward voltageI SEG = segment current set by R SET Dissipation Example:I SEG = 40mA, N = 8, DUTY = 31/32, V LED = 1.8V at 40mA, V+ = 5.25V PD = 5.25V(8mA) + (5.25V - 1.8V)(31/32 x 40mA x 8) = 1.11WThus, for a CERDIP package (θJA = +60°C/W from Table 12), the maximum allowed ambient temperature T A is given by:T J(MAX)= T A + PD x θJA + 150°C = T A +1.11W x60°C/Wwhere T A = +83.4°C.Cascading DriversThe example in Figure 3 drives 16 digits using a 3-wire µP interface. If the number of digits is not a multiple of 8, set both drivers’ scan limits registers to the same number so one display will not appear brighter than the other. For example, if 12 digits are need, use 6 digits per display with both scan-limit registers set for 6 digits so that both displays have a 1/6 duty cycle per digit. If 11 digits are needed, set both scan-limit registers for 6digits and leave one digit driver unconnected. If one display for 6 digits and the other for 5 digits, the sec-ond display will appear brighter because its duty cycle per digit will be 1/5 while the first display’s will be 1/6.Refer to the No-Op Register section for additional infor-mation.MAX7219/MAX7221______________________________________________________________________________________11Table 11. R SET vs. Segment Current and LED Forward VoltageTable 12. Package Thermal Resistance DataM A X 7219/M A X 722112______________________________________________________________________________________Figure 2. MAX7219/MAX7221 Driving 2.3-Inch DisplaysMAX7219/MAX7221______________________________________________________________________________________13Figure 3. Cascading MAX7219/MAX7221s to Drive 16 7-Segment LED DigitsM A X 7219/M A X 722114_______________________________________________________________________________________Ordering Information (continued)___________________Chip TopographySEG FSEG ACLK LOAD OR CS DIG 1DIG 5GNDGNDDIG 7DIG 3DIG 2DIG 60.093"(2.36mm)0.080"(2.03mm)SEG B ISET SEG ESEG DP SEG CSEG G DIG 4DIG 0DIN DOUT SEG DTRANSISTOR COUNT: 5267SUBSTRATE CONNECTED TO GNDMAX7219/MAX7221______________________________________________________________________________________15________________________________________________________Package InformationM A X 7219/M A X 7221___________________________________________Package Information (continued)Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.16____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600©1997 Maxim Integrated ProductsPrinted USAis a registered trademark of Maxim Integrated Products.。
